Current work deals with evaluating the effects of cholera enterotoxin (CE) on normal and neoplastic cells. The study addreses itself to two questions. In the first we are attempting to examine the possibility that macro or micro pinocytosis is involved in the entry of the active moiety of CE to the cells. We are attempting in this study to measure, with specific molecular probes, rates of macro and micro pinocytosis in normal and intoxicated cells and to see whether we can correlate rates of intoxication with the rate of pinocytosis. We are also interested in examining the detailed molecular events of the ADP ribosylation of the GTPase, in the action of toxin. We have found a light activated GTPase which is also ADP ribosylated by CE in the photoreceptor system. This enzyme is analogous to the epinephrine activated GTPase which is ADP ribosylated in the hormone sensitive cyclase. In the photoreceptor system there are additional heat labile trypsin sensitive factors involved in GTPase function and we are interested in studying the interaction of cholera toxin with these factors. These studies are aimed at learning more about the mechanism by which toxin enters the cell; the mechanism by which changes in enzymatic activity are achieved; and possible differences (both structural and functional) between normal and neoplastic membranes.